There is a detecting unit that detects the physical state of a subject by using the state of a subject's pulse or heartbeat. For example, the detecting unit arranged in a vehicle detects the physical state of a driver and thus reduces the occurrence of accidents caused by deterioration of the physical state of the driver.
For example, the detecting unit measures a potential difference signal between two electrodes that are brought into close contact with a subject and identifies, from the measured potential difference signal, an electrocardiographic signal that indicates the subject's pulse or heartbeat. Then, the detecting unit detects drowsiness or the degree of wakefulness as the subject's physical state by using the identified electrocardiographic signal.
For example, the electrodes that are brought into contact with the subject are arranged on, for example, a steering unit (steering wheel) or a seat surface in a vehicle. The electrodes arranged on the seat surface are brought into contact with the buttocks of the subject when the subject sits on the seat. The electrodes arranged at the steering wheel are brought into contact with the hands of the subject when the subject holds the steering wheel.
There is a processing unit that performs a reduction process for reducing noise contained in a potential difference signal. A vehicle in which the processing unit is arranged includes an electrode that is used as the reference electric potential, an electrode arranged on the steering unit, and an electrode arranged on a seat surface. The processing unit measures a potential difference signal between the electrode that is used as the reference electric potential and the electrode arranged on the steering unit and measures a potential difference signal between the electrode that is used as the reference electric potential and the electrode arranged on the seat surface. Then, the processing unit calculates the difference between the two potential difference signals to reduce the noise contained in the potential difference signal.
Furthermore, there is an apparatus that calculates heartbeat intervals for each heartbeat and then calculates the square mean value (root mean square of successive difference) of a standard deviation or a serial difference of the heartbeat intervals to remove irregular heartbeat intervals from the calculated heartbeat intervals.
Patent Literature 1: Japanese Laid-open Patent Publication No. 2009-142576
Patent Literature 2: Japanese Laid-open Patent Publication No. 2006-198403